The present invention relates generally to control of the operating height of a header of a mobile harvester or other farm implement. In particular, the present invention relates to a system for automatic height control responsive to ultrasonic range finding means which measures the distance to the top of the crop just forward of the header as the harvester or other farm implement is directed through the crop.
Harvesting of crops using modern, automated machinery can be onerous and tiring with the machinery used being large, heavy and highly complicated. In addition to guiding the harvester or other farm implement, such as a tractor, to which the header is attached, the operator has to be aware of various other operations and conditions which require independent action and reaction by the operator. It has heretofore been realized that it would be highly desirable to provide an automatic header height control system to aid the operator of the harvester in maintaining the header at an optimium operating height. Typical systems which have been proposed incorporate mechanical sensors or feelers. In one type of system, one or more ground following mechanical sensors or feelers are used to control a hydraulic or other power lift means for varying the height of the header relative to the ground directly beneath the header. See for example U.S. Pat. Nos. 3,908,345; 4,307,560; 4,312,177; 4,327,540; 4,332,126; and 4,354,555. These systems are responsive to changes in ground contour but otherwise operate on the assumption that the crop grows to a uniform height above the ground.
In a more direct attempt to determine the height of the crop itself researchers from the University of Saskatchewan, Saskatoon, Canada reported of their work in a paper entitled "An Automatic Height-of-Cut Control System For Windrowing" which was presented to the 1973 Annual Meeting of American Society of Agricultural Engineers (Paper No. 73-155). In this work, a sensor was located above the table canvas. The sensor consisted of two steel levers attached to microswitches. The microswitches are adapted to be activated by the cut crop as it falls on the table canvas behind the reel of the harvester. The system, unfortunately, suffered from mechanical instability and crop flow interference.
Numerous other disclosures of guidance systems for self-propelled vehicles including farm equipment are found in the patent literature. Generally, the proposed guidance systems operate in response to actuation of some type mechanical feeler means which generally engages a furrow, trench or other tracking means formed by or supported on the ground. Examplary of such disclosures are the following:
U.S. Pat. Nos.: 2,068,403; 3,039,554; 3,180,280; 3,188,978; 3,254,608; 3,402,787; 3,492,949; 3,537,531; 3,581,838; 3,708,019; 3,765,501; 3,797,602; 3,844,372; 3,946,825; 3,982,602; 4,161,143; 4,165,796; 4,184,551; 4,219,093; 4,301,739; 4,304,316; 4,366,756.
In a paper entitled "Swather Edge Guide Control System" which was presented to the 1975 Annual Meeting of the American Society of Agricultural Engineers (Paper No. 75-1029), researchers again from the University of Saskatchewan, Saskatoon, Canada, reported on a program to develop an automatic steering control system for a self-propelled swather. Three types of sensors were reported as being tested and evaluated. First, the electromechanical (feeler type) sensors of the prior art were considered undesirable inasmuch as they required contact with the crop edge and were prone to excessive wearing and ultimate malfunction. Second, ultrasonic sensors were found to completely fail to obtain sufficient reflection from the crop edge and, thus, were reported as being unfunctional and completely inoperative. Third, infrared photoelectric sensors were found capable of giving a good indication of the position of the crop. Inherent problems with the infrared sensing system were found to be accumulation of dirt on the infrared source and the sensor, and the variation in the output of the sensors in response to the color of the crop. The latter problem was caused by more infrared radiation being reflected from lighter colored crops than from darker colored crops.
An ultrasonic linkage system which was developed to link an operator-controlled tractor to an automatically controlled tractor in a master-slave mode was reported in Paper No. 76-1072 entitled "Ultrasonic Linkage for Tractor Guidance" which was given at the 1976 Annual Meeting of the American Society of Agricultural Engineers. The researchers, again from the University of Saskatchewan in Saskatoon, Canada, found that the slave tractor could be controlled using multiple sonic paths using tuned transmitters and receivers for initiating and receiving the sonic signals.
Sonar has for some time been used for depth indications for bodies of water and is widely used in shipping and ocean exploration. However, such usages of sonar do not suggest utilization of sonar means to activate a guidance mechanism for automatically controlling the height of a header on a mobile harvester or other piece of farm equipment in response to ultrasonic range finding means which measures the distance to the top of the crop just forward of the header. For automatic guidance of headers on farm machinery, the accuracy of the sonar guidance apparatus over short ranges must be quite high and the need for fast response and elimination of noise interference is essential.